Carotenoids, are a group of red and yellow pigments contained in plants and fruits. Carotenoids include carotenes and hydroxylated carotenoids designated xanthophylls. Xanthophylls include lutein, zeaxanthin, capsorubin, capsanthin, astaxanthin, and canthaxanthin.
The animal feed industry, the food industry, and the pharmaceutical industry have all indicated a strong interest in xanthophylls. The poultry industry receives a benefit in adding the xanthophylls to enhance the yolk color of eggs. The pharmaceutical companies have found that xanthophylls are useful in certain tumor treatments and as an antioxidant. The food industry has found that consumers are looking for naturally-occurring food colorants. Annatto, saffron, and paprika are a few natural carotenoids that have traditionally been used for food coloring. The dramatic red and yellow coloration and the xanthophylls' natural occurrence in edible plants such as green vegetables and fruit, for example, broccoli, green beans, peas, brussels sprouts, cabbage, kale, spinach, kiwi, and honeydew, have led to many uses, including a pigmentation additive for animal feeds. In certain vegetables, the xanthophylls are in the free non-esterified form. However, the large quantities of chlorophylls in green vegetables makes concentration or extraction of the xanthophylls difficult. A number of xanthophylls are also present in yellow-colored fruits and vegetables, such as mangoes, peaches, prunes, acorn squash, and oranges. These contain fewer chlorophylls, but often the xanthophylls exist in the esterified form with fatty acids such as myristic, lauric, and palmitic acids. Thus, to be metabolized in a feed additive, the xanthophylls' ester must undergo conversion to the free xanthophylls which is then metabolizable by the organism.
Although these various plant materials contain xanthophylls, the desired xanthophylls will drive the selection of the material used. For example, it is well known to use the petals of the marigold flower, Tagetes erecta, for the extraction of the lutein xanthophylls. Marigolds are readily cultivated and have been used as a pigment source for poultry. Lutein occurs in the marigold flower, diacylated with palmitic and myristic acids in long, fatty acid esters, typically as diesters in the chromoplastids.
The animal feed industry has taken two different approaches to providing xanthophylls in animal feeds, particularly lutein to poultry feeds. The industry had used the dried marigold meal as a feed additive, thus providing the lutein in the less useable acylated form. This form of the xanthophylls requires more consumption of the marigold meal to get the pigment desired. Alternatively, the industry has used a number of processes, starting with the extraction of the xanthophylls from the plant material and the formation of oleoresins. The industry then goes further and processes the oleoresins to convert the xanthophylls from the acylated form to the free form by a number of different processes, including transesterification for some oleoresin processing of paprika, though for lutein the process is primarily by saponification. The converted oleoresin requires less consumption by the animal to get the desired xanthophylls. However, formation of oleoresins and the processing thereof by saponification is both time-consuming and adds labor costs to the feed product.
Saponification is the conversion of the fatty acid into a soap by treating it with an alkali. The saponification number is the number of milligrams of potassium hydroxide required to saponify one gram of the ester. After saponification, the industry has often used solvents to crystallize the lutein from the oleoresin. This has made the xanthophylls more purified and available to the organism consuming the lutein, but it has added time and labor to the process of supplying the xanthophylls to the feed mixture.
Some of the following patents indicate the processes for recovering various compounds such as xanthophylls from oleoresins. U.S. Pat. No. 5,602,286 describes a process for recovering xanthophylls from corn gluten. The patent has the steps of adding ethanol as an extraction step, filtering, stripping to form the crude xanthophyll, and then using ethanol, using KOH as the sponification step, washing and filtering, then purifying to the refined xanthophylls.
Three Japanese references also show the use of similar oleoresin extractions. No. 82,133,160 Japan (1982) shows a red pepper pigment production using a red pepper oleoresin, in either water or alcohol-mixtures, treated with KOH, NaOH, CaCO.sub.3, and then treated with acids such as HCl, H.sub.2 SO.sub.4, H.sub.3 PO.sub.4, HOAc, lactic and citric acids. The pigment solutions are removed with organic solvents such as MeOH, EtOH, PrOH and acetone.
Patent No. 82,180,663 (1982), shows paprika food coloring agents that are extracted as an oleoresin. The oleoresin is heated with basic alkali metal compounds such as KOH, NaOH, K.sub.2 CO.sub.3, Na.sub.2 CO.sub.3, or sodium alcoholate, and mixed with one or more hydroxides, carbonates, or alkali earth metals, such as Ca(OH).sub.2. The precipitates are extracted with organic solvents and yield an odorless oleoresin pigment. Patent No. 83,173,164 shows paprika pigments can be prepared by treating paprika oleoresin with alkali at temperatures below 50.degree. C. in the presence of halogen ions, sulfates, bicarbonate, carbonate, phosphate, and aliphatic carboxy ions, then treated with an organic solvent, and, finally, extracted with acetone.
The U.S. Pat. No. 5,382,714 describes a method of producing substantially pure lutein. In this patent, the starting material was marigold petals. The process of saponification of the petals is briefly described in column 5, example 1. The flower petals were tested for herbicides and pesticides and then the xanthophyll-containing material was subjected to saponification with aqueous potassium hydroxide. This was accomplished by continuous mixing under heat (65-70.degree. C.) of food grade potassium hydroxide 45%. This accomplished the conversion of 98% of lutein into a form which was free of fatty acids and present as a yellow oil. This material could then be used as a feed or food additive.
The present invention provides a method of in situ conversion of the xanthophylls into the free form by liberation of the xanthophylls by transesterification; thus avoiding the need for the formation of the oleoresin. This oleoresin conversion requires an organic solvent extraction of the plant material; hexane is often used. The present invention provides in situ free-form xanthophylls by transesterification of in situ material, thus eliminating the need for an oleoresin or saponification of the material. The present invention allows the marigold meal to be subjected to transesterification and then used, without the extraction of the xanthophylls from the meal.